1. Field of the Invention
The present invention relates to a power transmitting device for a stepping motor and a disk drive provided with the power transmitting device.
2. Description of the Related Art
Conventionally, there has been generally known a disk drive provided with a disk transferring mechanism (i.e., a loading/ejecting mechanism) for transferring a disk between a loading position above a turn table and an ejection position outside of the device, as a disk drive for recording or reproducing an information signal in a disk serving as an information recording medium such as a so-called CD or DVD.
In the disk drive of such a type, a motor for driving the above-described disk transferring mechanism is needed in addition to a motor for turning and driving the turn table and a drive motor for performing a pickup moving operation so as to write and read a signal in a disk, and therefore, three motors in total are normally required to be mounted in the disk drive.
In contrast, for example, Japanese Patent Laid-open Publication No. 5-128688 discloses a configuration, in which one motor is configured such that its rotating force can be selectively transmitted to a side of a disk transferring mechanism or a side of a pickup moving mechanism, and the transmission of the rotating force of the motor is securely switched at a good timing, so that a disk transferring operation and a pickup moving operation are securely switched at a good timing, wherein one motor can serve as both of a drive source for the disk transferring mechanism and a drive source for the pickup moving mechanism, in order to reduce the number of motors to be used so as to reduce a cost and simplify the structure of the device. In the above-described prior art, the rotating force of the motor to the disk transferring mechanism and the pickup moving mechanism is transmitted via a gear system. The transmission of the rotating force of the motor is switched by switching the engaging state of the gear system.
The above-described pickup moving mechanism, is normally configured such that a feed screw is provided on a drive shaft extending along a pickup moving direction (i.e., the radial direction of the disk), an engaging element integral with a pickup engages with the feed screw, the feed screw is rotated by rotating the drive shaft by means of the motor, and thus, the pickup is moved along the feed screw. In the prior art, as is disclosed in, for example, the aforementioned gazette, it has been general that a so-called DC motor is used as a drive source and the drive shaft of the pickup moving mechanism is linked to the output shaft of the DC motor via a gear deceleration mechanism.
A disk drive in recent years has been required to move the pickup at a higher speed, as is represented by, for example, a disk drive applicable to a navigation system. However, in the prior art, a drive system of the pickup moving mechanism is configured such that the deceleration gear mechanism is combined with the so-called DC motor, so that there is a limit in achieving a high speed of the pickup movement.
Thus, in place of the configuration according to the prior art, it is considered to use a so-called stepping motor capable of rotating at a high speed and finely controlling the rotation is used as a drive source, and to transmit the power (i.e., the rotating force) of the stepping motor directly (in other words, without using any deceleration gear mechanism) to the drive shaft of the pickup moving mechanism.
As well known, the above-described stepping motor can finely control the rotation at a high speed, and therefore, it is remarkably suitable for the drive source for the pickup moving mechanism, in which a higher speed is required. However, in the case where a relatively heavy load is exerted at the beginning of the drive and at a very low engine speed, a step out, for example, is liable to occur. In that case, the stepping motor raises a drawback of relative difficulty in smooth and stable control.
The above-described disk transferring mechanism is adapted to basically at least drive a roller for transferring a disk or a rack for transferring a disk tray since the power of the motor serving as the drive source is transmitted via the deceleration mechanism such as the deceleration gear mechanism. Therefore, the disk transferring mechanism suffers a considerably heavy load ill comparison with the case where the pickup moving mechanism is driven.
Consequently, in the case where the stepping motor is used as the drive source for the pickup moving mechanism in order to achieve a high speed of the movement of the pickup, there arises a problem of a difficulty in reducing the number of motors used in the disk drive by means of a single motor (i.e., a single stepping motor) commonly serving as both of the drive source for the disk transferring mechanism and the drive source for the pickup moving mechanism, as described above. That is to say, when the stepping motor is driven in the state in which a motor power transmitting path is switched from the side of the pickup moving mechanism to the side of the disk transferring mechanism, a heavy load is exerted at the beginning of the drive and at a low engine speed, and therefore, it becomes difficult to stably perform a smooth control.
In view of the characteristics of the drive of the stepping motor, such a problem is inevitable not only in the case of the pickup moving mechanism and the disk transferring mechanism in the disk drive but also in various other cases where the stepping motor is commonly used as the drive source so that operation of a relatively light load and operation of a relatively heavy load are selectively performed by switching the power transmitting path.